1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a shield provided around a main magnetic pole, and a method of manufacturing the same.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Typically, magnetic heads for perpendicular magnetic recording have such a structure that a read head having a magnetoresistive element (hereinafter, also referred to an MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate, as is the case with magnetic heads for longitudinal magnetic recording. The write head includes a main magnetic pole that produces a magnetic field in a direction perpendicular to the plane of the recording medium. The main magnetic pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a nearly uniform width. To achieve higher recording density, it is required that the write heads of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as an overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end and an air outflow end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air outflow end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits a better capability of writing on a recording medium compared with the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erase). To increase the recording density, it is required to prevent the occurrence of adjacent track erase.
One of known techniques for preventing the occurrence of adjacent track erase resulting from the skew is to form the main magnetic pole such that its end face located in the medium facing surface has a width that decreases with decreasing distance to the top surface of the substrate, as described in U.S. Patent Application Publication No. 2007/0177301 A1 and U.S. Pat. No. 6,954,340 B2, for example.
Another effective technique for preventing the occurrence of adjacent track erase resulting from the skew is to provide two side shields on opposite sides of the main magnetic pole in the track width direction, as described in U.S. Patent Application Publication No. 2007/0177301 A1. It is also effective to provide a shield having an end face that is located in the medium facing surface and wraps around the end face of the main magnetic pole (such a shield will hereinafter be referred to as a wrap-around shield), as described in U.S. Pat. No. 6,954,340 B2. The wrap-around shield includes a bottom shield that is located on the air-inflow-end side relative to the main magnetic pole, a top shield that is located on the air-outflow-end side relative to the main magnetic pole, and two side shields that are located on opposite sides of the main magnetic pole in the track width direction. These techniques allow taking in a magnetic flux that is generated from the end face of the main magnetic pole and expands in the track width direction. This makes it possible to prevent the occurrence of adjacent track erase.
Now, methods for forming a main magnetic pole and two side shields will be considered. There are two broad categories of methods for forming a main magnetic pole and two side shields: one is to form the main magnetic pole first and form the two side shields thereafter; the other is to form the two side shields first and form the main magnetic pole thereafter.
An example of the method where the main magnetic pole is formed first and the two side shields are formed thereafter is as follows. First, the main magnetic pole and a nonmagnetic layer for accommodating the main magnetic pole are formed. Then, part of the nonmagnetic layer is etched to form two grooves for accommodating the two side shields. The two side shields are then formed by, for example, plating, such that they are accommodated in the two grooves. Where plating is employed to form the two side shields, seed layers are formed before plating is performed. This method will hereinafter be referred to as a first method.
An example of the method where the two side shields are formed first and the main magnetic pole is formed thereafter is described in U.S. Patent Application Publication No. 2007/0177301 A1. According to the method, a shield layer to later become the two side shields is formed first by, for example, plating. Then, part of the shield layer is etched to form a trench penetrating the shield layer. The shield layer thereby becomes the two side shields. Next, the main magnetic pole is formed to be accommodated in the trench. This method will hereinafter be referred to as a second method.
The following problem arises with the first method if the two side shields are formed by plating. In this case, the seed layers are formed to extend along the respective bottoms and wall faces of the two grooves. Plating films grow from the surfaces of the respective seed layers. Each of the plating films includes a portion grown from the portion of the seed layer extending along the bottom of the groove and a portion grown from the portions of the seed layer extending along the wall faces of the groove. These two portions meet each other to form a seam therebetween. The seam is a large grain boundary. Impurities are apt to segregate on the seam. The seam is therefore prone to be inferior in magnetic properties to other areas of each of the plating films, and thus can result in a magnetic defect. In the area near of the position of the magnetic defect in each of the plating films or side shields, magnetic flux is unstable and the direction of magnetization tends to be pinned. As a result, a large magnetic field can be generated locally in the side shields, which can result in the occurrence of adjacent track erase.
Additionally, if the first method is employed, an etching residue resulting from a reaction product produced during etching or resulting from a material etched may remain on the bottom of each of the grooves formed by etching. If the seed layer is formed on the etching residue, the seed layer will have a projection at the position of the etching residue. In the area of each of the plating films or side shields near the projection of the seed layer, magnetic flux is unstable and the direction of magnetization tends to be pinned, as with the magnetic defect caused by the seam. Therefore, it may be said that the area of each of the plating films near the projection of the seed layer can also result in a magnetic defect. The magnetic defect can locally generate a large magnetic field in the side shields, which can result in the occurrence of adjacent track erase.
In the first method, the two grooves for accommodating the two side shields are formed by etching. The shapes of the two side shields are thereby determined. Typically, patterning of a layer by using etching requires a larger number of process steps and more time than in the case of patterning of a layer by using only photolithography. The first method therefore has the problem of high cost in manufacturing magnetic heads because of the need for a large number of process steps and much time to determine the shapes of the two side shields.
In the second method, the shapes of the two side shields are determined by etching. This means that the second method also requires a large number of process steps and much time to determine the shapes of the two side shields, and therefore has the problem of high cost in manufacturing magnetic heads.
On the other hand, the following problem arises if the main magnetic pole is shaped such that its end face located in the medium facing surface decreases in width with decreasing distance to the top surface of the substrate. If the main magnetic pole of such a shape is formed by a conventional method of forming a main magnetic pole, major part of the side surface of the main magnetic pole along the entire perimeter of the main magnetic pole is formed into a tilt surface tilted with respect to a direction perpendicular to the top surface of the substrate. The main magnetic pole of this shape is smaller in cross-sectional area perpendicular to the direction in which magnetic flux flows, compared with a case where the entire side surface of the main magnetic pole is perpendicular to the top surface of the substrate. The main magnetic pole of the foregoing shape cannot allow much magnetic flux to pass, especially through a part near the boundary between the track width defining portion and the wide portion. This results in degradation of write characteristics such as overwrite property.
An effective technique for solving this problem is, as disclosed in U.S. Patent Application Publication No. 2008/0239567 A1, to form the main magnetic pole into the following shape. The main magnetic pole formed by the technique disclosed therein has first and second side surfaces that are opposite to each other and located in a first region extending from the medium facing surface to a position at a predetermined distance from the medium facing surface, and third and fourth side surfaces that are located in a second region other than the first region. The main magnetic pole further has a fifth side surface located in the boundary between the first and second regions and connecting the first side surface to the third side surface, and a sixth side surface located in the boundary between the first and second regions and connecting the second side surface to the fourth side surface. The distance between the first side surface and the second side surface in the track width direction decreases with decreasing distance to the top surface of the substrate. In the boundary between the first region and the second region, the distance between the third side surface and the fourth side surface in the track width direction as seen at the position closest to the top surface of the substrate is greater than the distance between the first side surface and the second side surface in the track width direction as seen at the position closest to the top surface of the substrate. Each of the fifth and sixth side surfaces has a width that increases with decreasing distance to the top surface of the substrate. This technique allows the main magnetic pole to have a large cross-sectional area perpendicular to the direction of flow of the magnetic flux in the vicinity of the boundary between the track width defining portion and the wide portion, thereby allowing much magnetic flux to pass. As a result, it is possible to improve write characteristics such as overwrite property.
If a magnetic head with a wrap-around shield and a main magnetic pole of the foregoing shape is to be formed by the conventional manufacturing method, a large number of process steps and much time are required to determine the shapes of the two side shields and the main magnetic pole. This results in higher costs in manufacturing the magnetic head.